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location Stockholm, Sweden
age 29
visits member for 4 years, 11 months
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I am interested in the moduli space of curves and also other things. I am currently on parental leave.


20h
comment Map between stacks and automorphism groups
Your question has already been answer but let me give a really lowbrow comment. It's sometimes useful to think of a point with isotropy group of order $\vert G \vert$ as "$1/\vert G \vert$th of a point". So for instance if you have point of $M_g$ corresponding to a curve with no automorphisms, and it maps to its jacobian in $A_g$ which has the inversion automorphism, then this corresponds to "a whole point" mapping to "half of a point". This makes the map 2-to-1 in the sense of stacks.
1d
comment A functorial isomorphism in derived category
I don't think $j$ necessary takes values in $K^+(\mathcal B)$. Look at stacks.math.columbia.edu/tag/0140
2d
comment A functorial isomorphism in derived category
Why do you think my answer (to the other question) is not functorial? The truncations $\tau_{\geq n}$ are certainly functorial, and a zig-zag of quasi-isomorphisms in $\mathrm{Ch}(\mathcal A)$ defines functorially a morphism in $D(\mathcal A)$. And as Mariano remarks, injective resolutions can be made functorial under mild hypotheses on $\mathcal A$ (certainly satisfied for sheaves on spaces).
Oct
16
awarded  Nice Answer
Oct
14
comment Two basic questions on derived categories
I agree that both constructions should be functorial.
Oct
13
comment Name for series $\sum f_n x^n / (n! (n+k)!)$
I guess the case $k>0$ arises naturally as the $k$th derivative of a doubly exponential generating function. This would seem to reduce the study of "Bessel" generating series to that of doubly exponential ones.
Oct
13
revised Two basic questions on derived categories
deleted 1 character in body
Oct
13
answered Two basic questions on derived categories
Oct
10
comment When is the Hodge diamond concentrated in $H^{n,n}$'s?
One example where the even cohomology is spanned by algebraic cycles and the odd cohomology is nonzero is the moduli space $\overline M_{1,n}$ of $n$-pointed stable curves of genus one, which has odd cohomology for $n\geq 11$.
Oct
9
comment When is the Hodge diamond concentrated in $H^{n,n}$'s?
See the question mathoverflow.net/questions/151341
Oct
8
revised Why Weil group and not Absolute Galois group?
deleted 5 characters in body
Oct
1
comment $H^4(BG,\mathbb Z)$ torsion free for $G$ a connected Lie group
Don't you need $G$ to be simply connected to apply the Hurewicz theorem?
Oct
1
answered Standard homology result on double complexes
Oct
1
comment (Very) High dimensional manifolds
Actually it seems the authors only prove that their example has minimal rank, not minimal dimension. Still a very nice answer.
Sep
30
awarded  Explainer
Sep
29
revised Connected components of the complement of a degree-d affine hypersurface
added 2 characters in body
Sep
29
reviewed Approve suggested edit on Connected components of the complement of a degree-d affine hypersurface
Sep
29
answered Connected components of the complement of a degree-d affine hypersurface
Sep
28
revised Holomorphic cusp forms and cohomology of GL(2,Z)
added 893 characters in body
Sep
28
accepted Holomorphic cusp forms and cohomology of GL(2,Z)